Asteroseismologie

Asteroseismologie is the study of oscillations in stars to infer their internal structure and dynamics. By observing natural pulsations, scientists probe conditions in stellar interiors that are otherwise inaccessible. Oscillations are commonly categorized as pressure modes (p-modes), which are driven by pressure forces, gravity modes (g-modes), driven by buoyancy, and mixed modes that occur in evolved stars, coupling p- and g-mode character.

Observationally, asteroseismologie relies on time-series measurements of stellar brightness or spectral lines. Space-based photometry from missions such as CoRoT, Kepler, K2, and TESS provides high-precision light curves; ground-based spectroscopy adds radial velocity data. Frequencies are extracted with Fourier transforms, and patterns of multiplets reveal mode degrees and radial orders.

From the frequency spectrum, fundamental properties are inferred. The large frequency separation Δν scales with the square root of mean density, roughly Δν ≈ (M/R^3)^0.5, while the frequency of maximum power νmax scales with surface gravity and effective temperature. Small separations probe core structure and age. In evolved stars, mixed modes reveal core rotation and composition.

Asteroseismologie builds on helioseismology and has grown with space-based observations delivering precise ages, masses, and radii for many stars. It is essential for characterizing exoplanet host stars and for studying stellar evolution, Galactic archaeology, and internal rotation.

Challenges include mode identification, short mode lifetimes, and surface effects that bias frequencies. Modeling uncertainties in convection, opacities, and overshoot affect interpretations. Ongoing improvements come from better data, advanced modeling, and combining seismic information with spectroscopy.